Sexuality

ranscription factor, BTB-ZF family
    A gene called "fruitless" was identified in fruit flies in the 1970's which influences sexual preference.  Males with the gene mutation are unable to discriminate between the sexes, engaging both male and female flies in courtship behaviors.  Males with severe mutations in fruitless lose interest in sex altogether.  When confronted with cues that elicit sexual behavior in normal males, fruitless males fail to follow female flies, play courtship songs on their wings, or attempt copulation.  The fruitless gene codes for a transcription factor expressed in fruit fly brain cells that plays a role in turning other genes on and off. Roush, Science, 274:1836, 1996; Ryner et al., Cell, 1079, 1996; Villella et al., Genetics, 147:1107-1130, 1997.

Xq28 + [HGL]
    A certain DNA marker on the Xq28 region of the X chromosome was correlated with male homosexuality.  Males in the family who had inherited a X chromosome from their mother bearing this signpost were more likely to be gay than their male relatives who had not.  Hamer et al., Science, 261:321, 1993.   Since the publication of this work, other groups have been unable to repeat it, making the "gay" gene controversial, but not dead. Wickelgren, Science, 284: 571, 1999; Rice et al., Science, 284:665-667, 1999. The original researchers still stick by their data.  Hamer, Science, 285:803, 1999.

Affiliative behavior
arginine vasopressin (AVP) receptor, subtype 1a (V1a-receptor) [GE]
    Arginine vasopressin (AVP) is an amino acid neurotransmitter involved in many species-typical behaviors, including male social behaviors, communication, aggression, sexual behavior, and in monogamous species, pair bonding and parental care.  The effects of AVP are mediated by the V1a-receptor, a member of a family of G-protein coupled receptors.  When AVP is injected into the brain of a male, monogamous, prairie vole, it displays increased affiliative behavior to a stimulus female.  Injection of AVP into the brain of a male, polygamous montane vole had no effect.  The effect of AVP appears to be related to its distribution in the brain since the receptor has the same binding characteristics in each vole type but has strikingly different patterns of expression in the brain.  Transgenic mice were created which expressed the prairie vole V1a receptor.  The brains of such mice had a similar pattern of expression as the brain of a prairie vole but different from the montane vole.  Like the prairie vole, injection of AVP into the transgenic mice increased affiliative behavior.  This supports the theory that the species different distribution of the V1a receptor accounts for the affiliative response to AVP.  Young et al, Nature, 400:766-768, 1999.